Method and apparatus for autofocusing a microscope

Abstract

An autofocusing microscope includes a spot marker assembly for projecting a spot marker on the sample surface. The image of the spot marker is continuously scanned while the objective lens is moved along a preselected range of distances from said sample surface. The lens is then moved to the optimum focusing in accordance with the scanning.

I claim: 
     
       1. An autofocusing microscope on a sample surface, said microscope having an objective lens comprising: means for generating a preselected image on a sample surface, the objective lens imaging the preselected image onto the surface;   means for scanning said preselected image at a plurality of objective lens positions;   means for selectively moving said objective lens along an optical axis of the microscope, the optical axis defined by a line passing through a central point in the sample surface and a central point in the objective lens in a preselected range of positions; and   means for determining an optimal position of said lens in accordance with the scanned preselected image.   
     
     
       2. An autofocusing microscope comprising: an objective lens movable along an optical axis of the microscope, the objective lens imaging the preselected image onto the surface;   means for projecting a spot marker along said optical axis to form an image on a sample surface;   means for scanning the image along said optical axis at a plurality of objective lens positions and generating scanning signals indicative of the focus of said image; and   control means connected to the scanning means for moving said objective lens to an optimum position in accordance with said scanning means.   
     
     
       3. The microscope of claim 2 wherein said control means comprises a signal processor and a motor for moving said lens along said optical axis. 
     
     
       4. The microscope of claim 3 wherein said signal processor is adapted to move said lens through a preselected range to determine the position which corresponds to a maximum rate of change of values of the scanning signal. 
     
     
       5. The microscope of claim 4 wherein said signal processor is adapted to store the scanning signals corresponding to each lens position within said range and to move said lens to the position corresponding to said maximum scanning signal. 
     
     
       6. The microscope of claim 2 wherein said objective lens is located and aligned for projecting the spot marker onto said sample surface. 
     
     
       7. The microscope of claim 6 wherein said objective lens is located and aligned for scanning said image. 
     
     
       8. The microscope of claim 2 wherein said means for scanning comprises a video camera. 
     
     
       9. The microscope of claim 8 wherein said means for scanning comprises an array of photodiodes. 
     
     
       10. The microscope of claim 2 wherein said means for generating a preselected image comprises a light source and a mask having an aperture corresponding to said spot marker. 
     
     
       11. A method of focusing microscope on a sample surface with an objective lens comprising: generating a spot marker;   projecting said spot marker through said objective lens unto the sample surface to form an image;   moving said objective lens along a preselected range;   scanning said image along a plurality of lens positions to generate scanning signals;   storing the scanning signals corresponding to positions of said lens within said range; and   moving said lens to the position corresponding to the maximum scanning signal.   
     
     
       12. The method of claim 11 comprising the step of providing an indication of the contrast of said image by said scanning signals.